FZJ-2013-04880
1
DFG/Transregio32 Acknowledgment to Transregional Collaborative Research Centre 32 (TR32; more information at http://www.tr32.de) and the Field and Laboratory Team of the IBG-3 Institute Influence of Seasonal Soil Moisture Patterns on Transit Time Distributions (TTDs) M. Stockinger 1* , H. Bogena 1 , A. Lücke 1 , B. Diekkrüger 2 , M. Weiler 3 and H. Vereecken 1 1 Agrosphere (IBG-3), Forschungszentrum Jülich GmbH, Jülich, Germany; 2 Geographical Institute, University of Bonn, Germany; 3 Institute of Hydrology, Albert- Ludwigs-University Freiburg, Freiburg, Germany *Corresponding author: [email protected] Precipitation travels via different pathways through a catchment to become groundwater or river water. The Transit Time Distribution (TTD) integrates travel times of precipitation water and is influenced by catchment characteristics (e.g. land use). The exact relations between catchment characteristics and the TTD are not fully understood yet. We present findings of the Wüstebach (Fig. 1), a forested headwater catchment (38.5 ha), and its tributary catchment NE (11 ha), showing and influence of soil moisture on spatial TTD patterns of gauged and ungauged river and tributary locations. Threshold Response To model ungauged locations, we first simulated runoff at the outlet (Eq. 1, Fig. 3a) to derive effective precipitation (p eff ). We found a different response during “summer” and “winter” (Fig. 2), defined by mean soil water content (SWCm) values lower or greater than a threshold of 35 Vol.% (Fig. 3b). Fig. 3: (a) Measured (grey) and simulated (black) runoff Q(t) in logarithmic scale. p eff as bars from top. Shown are also the modelling periods (vertical lines), (b) SCWm, also with modeling periods and (c) 18 O time series of precipitation (black) and river sampling locations (grey). Stream locations showed TTDs either close to the outlet’s TTD or much faster, while tributaries showed more diverse TTDs (Fig. 5). What determines TTDs? Summer Winter In winter, runoff reaction shows fast and slow components. During summer, there is only a fast reaction (Fig. 2). We argue that during summer the hillslope soils (cambisols) dry out due to evapotranspiration such as no p eff is generated anymore. The well- saturated riparian zone (5 ha) remains active in terms of runoff generation. Thus, the catchment area reduces to 5 ha in summer, while being 38.5 ha in winter. Hydrograph simulation has been performed by splitting the modeling time series into sub-time series according to the threshold SWCm. Calculation of TTDs 18 O was used as a tracer to derive TTDs as input from precipitation C in and output at 1 gauged river and 14 ungauged river and tributary locations, C(t). By simulating stream isotope values (Fig. 4), we can derive the respective TTD (h b (), Eq. 2) for each location (Fig. 5). As the Wüstebach is small and uniformly covered by spruce trees, we assume the time series of p eff to be spatially constant. Fig. 4: Measured (grey) and simulated (black) isotopes for the spring (location 1) and the outlet (location 14) of the catchment. Mean Transit Times of the isotope measurement locations show a negative correlation with the percentage of riparian zone within each respective sub-catchment (Fig. 6). Summary • Seasonal soil moisture patterns influence TTDs • Calculation of TTDs for ungauged locations is possible for a small catchment with the assumption of p eff = spatially constant. Fig. 1: The Wüstebach catchment and its tributary catchment to the NE. Fig. 2: The Wüstebach catchment and its tributary catchment to the NE. Eq. 1: Hydrograph simulation, with runoff Q simulated by convoluting p eff and response times (g()). Eq. 2: Isotope simulation, simulating stream isotopes C(t) with precipitation isotopes C in , p eff and the TTD h b (). Fig. 5: TTDs of all isotope measurement location. The outlet (red) integrates faster (solid) and slower (dashed) TTDs. Stream locations are highlighted in green. Fig. 6: Negative correlation between percentage of riparian zone and MTT of the sub-catchments of each respective measurement location.
description
- PowerPoint PPT Presentation
Transcript of FZJ-2013-04880
DFG/Transregio32
Acknowledgment to Transregional Collaborative Research Centre 32 (TR32; more information at http://www.tr32.de) and the Field and Laboratory Team of the IBG-3 Institute
Influence of Seasonal Soil Moisture Patterns on Transit Time Distributions (TTDs)M. Stockinger1*, H. Bogena1, A. Lücke1, B. Diekkrüger2, M. Weiler3 and H. Vereecken1
1Agrosphere (IBG-3), Forschungszentrum Jülich GmbH, Jülich, Germany; 2Geographical Institute, University of Bonn, Germany; 3Institute of Hydrology, Albert-Ludwigs-University Freiburg, Freiburg, Germany
*Corresponding author: [email protected]
Precipitation travels via different pathways through a catchment to become groundwater or river water. The Transit Time Distribution (TTD) integrates travel times of precipitation water and is influenced by catchment characteristics (e.g. land use). The exact relations between catchment characteristics and the TTD are not fully understood yet.
We present findings of the Wüstebach (Fig. 1), a forested headwater catchment (38.5 ha), and its tributary catchment NE (11 ha), showing and influence of soil moisture on spatial TTD patterns of gauged and ungauged river and tributary locations.
Threshold ResponseTo model ungauged locations, we first simulated runoff at the outlet (Eq. 1, Fig. 3a) to derive effective precipitation (peff). We found a different response during “summer” and “winter” (Fig. 2), defined by mean soil water content (SWCm) values lower or greater than a threshold of 35 Vol.% (Fig. 3b).
Fig. 3: (a) Measured (grey) and simulated (black) runoff Q(t) in logarithmic scale. peff as bars from top. Shown are also the modelling periods (vertical lines), (b) SCWm, also with modeling periods and (c) 18O time series of precipitation (black) and river sampling locations (grey).
Stream locations showed TTDs either close to the outlet’s TTD or much faster, while tributaries showed more diverse TTDs (Fig. 5).
What determines TTDs?
Summer
Winter
In winter, runoff reaction shows fast and slow components. During summer, there is only a fast reaction (Fig. 2).
We argue that during summer the hillslope soils (cambisols) dry out due to evapotranspiration such as no peff is generated anymore. The well-saturated riparian zone (5 ha) remains active in terms of runoff generation. Thus, the catchment area reduces to 5 ha in summer, while being 38.5 ha in winter.
Hydrograph simulation has been performed by splitting the modeling time series into sub-time series according to the threshold SWCm.
Calculation of TTDs18O was used as a tracer to derive TTDs as input from precipitation Cin and output at 1 gauged river and 14 ungauged river and tributary locations, C(t). By simulating stream isotope values (Fig. 4), we can derive the respective TTD (hb(), Eq. 2) for each location (Fig. 5).
As the Wüstebach is small and uniformly covered by spruce trees, we assume the time series of peff to be spatially constant.
Fig. 4: Measured (grey) and simulated (black) isotopes for the spring (location 1) and the outlet (location 14) of the catchment.
Mean Transit Times of the isotope measurement locations show a negative correlation with the percentage of riparian zone within each respective sub-catchment (Fig. 6).
Summary• Seasonal soil moisture patterns influence TTDs• Calculation of TTDs for ungauged locations is
possible for a small catchment with the assumption of peff = spatially constant.
Fig. 1: The Wüstebach catchment and its tributary catchment to the NE.
Fig. 2: The Wüstebach catchment and its tributary catchment to the NE.
Eq. 1: Hydrograph simulation, with runoff Q simulated by convoluting peff and response times (g()).
Eq. 2: Isotope simulation, simulating stream isotopes C(t) with precipitation isotopes Cin, peff and the TTD hb().
Fig. 5: TTDs of all isotope measurement location. The outlet (red) integrates faster (solid) and slower (dashed) TTDs. Stream locations are highlighted in green.
Fig. 6: Negative correlation between percentage of riparian zone and MTT of the sub-catchments of each respective measurement location.
